1. Field of the Invention
The present invention relates to a disk drive apparatus, and to a semiconductor integrated circuit device for use in a disk drive apparatus.
2. Description of the Prior Art
A conventional disk drive apparatus will be described. FIG. 1 shows the arrangement of various circuits in an LSI (large-scale integrated circuit) 60 designed for use in a floppy disk drive apparatus taken as an example of a conventional disk drive apparatus. The LSI 60 includes a stepping motor driver 11, an analog signal processing circuit 13, a controller 12, and a thermal shutdown circuit 23.
The stepping motor driver 11, by its on/off operation, feeds an electric current to a stepping motor (not shown) to drive it. The stepping motor serves to transport a read/write head (not shown) to a specified track position.
The analog signal processing circuit 13 processes analog signals that are communicated to write and read data to and from a floppy disk, which is a type of magnetic data recording medium. The controller 12 interfaces with a personal computer (not shown) serving as a host, and also controls the stepping motor driver 11 and the analog signal processing circuit 13.
The thermal shutdown circuit 23 incorporates a temperature monitoring circuit, with which it monitors the temperature of the LSI 60. As the stepping motor driver 11 operates, the LSI 60 generates heat. If the LSI 60 generates so much heat that its temperature rises above a predetermined temperature, the thermal shutdown circuit 23 forcibly turns off the stepping motor driver 11. Thus, the thermal shutdown circuit 23 serves to prevent malfunctioning of the LSI 60 due to high temperature resulting from abnormal heat generation and simultaneously protect the LSI 60 from abnormal heat generation.
FIG. 2 shows a part of the LSI 60. The thermal shutdown circuit 23 outputs a voltage that represents the monitored temperature. When this voltage rises above a threshold voltage, the thermal shutdown circuit 23 turns off the stepping motor driver 11.
Conventionally, as shown in FIG. 2, the stepping motor driver 11 and the thermal shutdown circuit 23 are arranged close to each other. As a result, as shown in FIG. 3, every time the stepping motor driver 11 is turned on or off as indicated by the waveform 73, a back electromotive force appears in the coil of the stepping motor (not shown) connected to the LSI 60, and this back electromotive force causes a current to flow through the IC substrate into the ground pattern of the stepping motor driver 11, the stepping motor driver 11 pulling the current in from its ground pattern. Consequently, the ground level VG around the stepping motor driver 11 suffers noise of about 0.1 V. In the temperature monitoring circuit, a constant current is made to flow through a resistor to use the voltage appearing across the resistor as a reference voltage VT, and this reference voltage VT is applied to the base of a transistor. As the temperature rises, the threshold voltage VF of the transistor drops; when the temperature becomes so high that VT exceeds VF, the transistor is turned on, and thereby indicates that the temperature has reached the predetermined temperature.
For example, as shown in FIG. 3, when, at a time point t1, the stepping motor driver 11 is turned from on to off, the ground level VG suffers noise 70. Since the reference voltage VT equals the voltage across the resistor (indicated by the waveform 71 in FIG. 3) added to the ground level VG, the noise 70 acts to shift up the reference voltage VT. This makes the temperature monitoring by the temperature monitoring circuit accordingly less accurate, and thus degrades the accuracy with which the thermal shutdown circuit 23 monitors the temperature.
To solve this problem, as shown in FIG. 2, in the conventional LSI 60, it is customary to minimize the effect of the noise by securing an inhibited region 15, about 200 .mu.m wide, around the stepping motor driver 11 and arranging the thermal shutdown circuit 23 outside the inhibited region 15. However, securing an inhibited region 15 in an LSI 60 inconveniently requires a larger chip area.